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Improving the nitrogen (N) utilisation efficiency (NUE) of dairy cows by breeding was considered beneficial for environmental footprints, feeding costs and animal health. Due to the difficult data obtainment of NUE, the cow-individual milk urea (MU) value was suggested as an indicator trait. MU data fulfills the requirements for the breeding value evaluation routine, but studies questioned a stable relationship to NUE. It became evident that a deeper knowledge on the underlying principles of cow-individual N utilisation and -excretion is indispensable before MU can be seriously considered for breeding strategies. In this context four studies were conducted, which focused on the host genome-trait, the host genome-rumen microbiota and the entire host genome-rumen microbiota-trait complex, aiming for a holistic exploration of cow-individual N utilisation and N excretion as a pre-step for future breeding strategies. The results of the studies and their overall interpretation let assume that genomic selection with MU would impact the host genome-rumen microbiota axis (i.e. the holobiont) which subsequently jointly affects MU and NUE- associated phenotypes. [ABSTRACT FROM AUTHOR]

The current project based on the hypothesis that environmental challenges contribute to genetic characteristics of west-African cattle breeds being associated with adaptation, robustness and heat tolerance. Furthermore, social-ecological transformations in the African context may initiate breeding processes towards improved productivity and product quality. For inferring the respective genomic mechanisms, 449 cattle of the local breeds Borgou, Pabli-Kerou, Lagune and Somba were genotyped using the 50K SNP chip. Based on the first two principal components, breeds could be clearly allocated to different clusters, displaying further sub-clusters for the respective historical populations. Obvious was the large genetic distance with high-yielding German cattle breeds such as HF. A particularity of the genomic studies addressing selection signatures was the possible contrasting with the respective historical populations to infer genetic processes of transformation by time. The annotated potential candidate genes contributed to physiological pathways and mechanisms inducing immunity and adaptation. The detected gene RNF220 has well-known effects on calving ease in HF. Genome-wide associations for measurements of morphological traits could be associated with heat tolerance and disease resistance. The quite large heritabilities for continuous body measurements in cm indicate potential for further optimizations of genetic evaluations for conformation traits. Whole-genome sequencing of the west-African breeds contributed to the detection of four novel milk protein variants, illustrating the importance of west-African genetic resources to improve product quality. [ABSTRACT FROM AUTHOR]